A positional tolerance controls the location of one feature from another feature or datum.
The tolerance zone can be the space between two parallel lines or planes, a circle, or a cylinder. The zone defines the permissible deviation of a specified feature from a theoretically exact position.
The tolerance value is the distance between the parallel lines or planes, or the diameters of the circle or cylinder.
The theoretically exact position also incorporates squareness and parallelism of the tolerance zones with the plane of the drawing.
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